1. Field of the Invention
The present invention relates to a friction engaging device such as a clutch or a brake that is incorporated in an automotive automatic transmission.
2. Description of the Related Prior Art
A friction engaging device comprises externally toothed discs each having outer circumferential teeth adapted to spline engage an outer member and internally toothed discs each having inner circumferential teeth adapted to spline engage an inner member, wherein the externally toothed discs and the internally toothed discs are brought into press contact with each other in an axial direction via friction materials for torque transfer between the outer member and the inner member.
In friction engaging devices as descried above, there are a double-side application type and a single-side application type. In the double-side application type, a first friction material adapted to be interposed between an externally toothed disc and an internally toothed disc that is located contiguously on one side of the externally toothed disc in an axial direction is attached to the other side of the internally toothed disc in the axial direction, whereas a second friction material adapted to be interposed between an internally toothed disc and an externally toothed disc that is located contiguously on one side of the internally toothed disc in the axial direction is attached to one side of the internally toothed disc in the axial direction. On the other hand, in the single-side application type, first and second friction materials are attached to one side of an externally toothed disc in the axial direction and one side of an internally toothed disc in the axial direction, respectively (refer to Japanese Patent Unexamined Publication No. Hei.10-78051).
In the double-side application type of friction engaging device, the sides of the externally toothed disc constitute friction surfaces for the first and second friction materials, and friction heat generated in the first and second friction materials is then introduced into the externally toothed disc from the sides thereof. This eventually increases the heat that is to be introduced into the externally toothed disc, and as a countermeasures against the heat so introduced, the externally toothed disc needs to be thicker to increase the heat capacity thereof, and as a result thereof, the axial length of the friction engaging device has to be made longer. On the other hand, in the single-side application type of friction engaging device, friction heat generated in the first and second friction materials is introduced into the externally and internally toothed discs in a dispersed fashion. Due to this construction, the respective discs do not need to be made thicker, and the axial length of the friction engaging device can be made shorter, whereby the friction engaging device can be made smaller in size and lighter in weight.
As described above, with the single-side application, although the thickness of the respective discs does not have to be made thicker, with a view to securing the strength of the outer circumferential teeth of the externally toothed discs and the inner circumferential teeth of the internally toothed discs, the thickness of the respective discs cannot be reduced beyond a predetermined limit, and this causes a problem in attempting to make the friction engaging device further smaller in size and lighter in weight.
The present invention was made in view of the above drawback inherent in the prior art friction devices, and an object thereof is to provide a friction engaging device which can be made further smaller in size and lighter in weight.
With a view to solving the aforesaid problem, according to a first aspect of the invention, there is provided a friction engaging device comprising externally toothed discs each having outer circumferential teeth adapted to be spline engaged with an outer member and internally toothed discs each having inner circumferential teeth adapted to be spline engaged with an inner member, wherein the externally toothed discs and the internally toothed discs are brought into axial press contact with each other via friction materials for performing the transfer of a torque between the outer member and said inner member, the friction engaging device being characterized in that one side face of each of the externally toothed discs in an axial direction is formed into a stepped surface having a raised surface portion on a radially outer side of the disc and a recessed surface portion on a radially inner side thereof by making a radially inner half portion of each of the externally toothed discs thinner than a radially outer half portion thereof, that the other side face of each of the internally toothed discs in an axial direction which is located contiguously to the one side of each of the externally toothed discs in the axial direction is formed into a stepped surface having a raised surface portion on a radially inner side of the disc and a recessed surface portion on a radially outer side thereof by making a radially outer half portion of each of the internally toothed discs thinner than a radially inner side half portion thereof, and that first friction materials interposed between the externally toothed discs and the internally toothed discs that are located contiguously to the one side of the externally toothed discs in the axial direction are each divided into a radially outer half portion and a radially inner half portion, the radially inner half portion of the first friction material being attached to the recessed surface portion on the one side of each of the externally toothed discs in the axial direction or the raised surface portion on the other side of each of the internally toothed discs in the axial direction, the radially outer half portion of the first friction material being attached to the recessed surface portion on the other side of each of the internally toothed discs in the axial direction or the raised surface portion on the one side of each of the externally toothed discs in the axial direction.
According to the first aspect of the invention, the thicknesses of the radially outer half portion of the externally toothed discs and the radially inner half portion of the internally toothed discs are made so sufficient to secure a required strength for the outer circumferential teeth of the externally toothed discs and for the inner circumferential teeth of the internally toothed discs, and on the other hand, the thicknesses of the radially inner half portion of each of the internally toothed discs corresponding to the radially inner half portion of the first friction material and the radially inner half portion of each of the internally toothed discs corresponding to the radially outer half portion of the first friction material are made as thin as possible irrespective of the strength of the teeth, whereby the axial length of the friction engaging device can be reduced. Thus, the friction engaging device can be made smaller in size and lighter in weight without deteriorating the strength of the teeth of the respective discs.
Additionally, according to a second aspect of the invention, there is provided a friction engaging device as set forth the first aspect, wherein one side of each of the internally toothed discs in the axial direction and the other side of each of the externally toothed discs in the axial direction which is located contiguously to the one side of each of the internally toothed discs in the axial direction are formed into a flat plane, wherein second friction materials interposed between the externally toothed discs and the internally toothed discs are each divided into a radially outer half portion and a radially inner half portion and wherein the radially inner half portion of the second friction material is attached to one of the externally and internally toothed discs to which the radially inner half portion of the first friction material is not attached, whereas the radially outer half portion of the second friction material is attached to one of the externally and internally toothed discs to which the radially outer half portion of the first friction material is not attached. This construction provides substantially a friction engaging device of the single-side application type, and is advantageous in attempting to make the size of the device smaller.